Telephone transmitter having frustoconical back electrode



Dec. 5, 1950 H. w. BRYANT TELEPHONE TRANSMITTER HAVING FRusTo-coNTcAL BACK ELECTRODT: Filed oct. 51, 1947 A 7' TURA/EV Patented Dec. 5, 1950 TELEPHONE TRANSMITTER HAVING FRUSTOCUNICAL BACK ELECTRODE Herbert W. Bryant, Chatham, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application Gotober 31, 1947, Serial N0. 783,324

12 Claims.

ters and more particularly to carbon granule type transmitter units especially suitable for use in hand telephones.

Transmitter units of the type to which this invention pertains comprise, in general, a carbon granule lled chamber bounded in part by a pair of electrodes one of which is coupled to a diaphragm to vibrate therewith in accordance with speech or other sound waves effective upon the diaphragm. The operating characteristics of such units are dependent upon the resistance of the current path, through the carbon granules, between the two electrodes and the manner in which this resistance Varies in response to vibrations of the diaphragm.

In order to obtain high modulation, it is desirable that the electrodes be relatively closely spaced. However, as the electrode spacing'is reduced, the tendency of the carbon granules to pack increases, with consequent degradation in the performance of the unit.

Further, transmitter units when included in hand telephones are subject to operation in a variety of positions. The gravitational forces upon the granules tend to vary the effective pressure between the'carbon granules and the electrodes with diiference in position of the unit, so that the operating characteristics of the unit may vary considerably with position in which the hand telephone is held.

One general object of this invention is to improve the operating characteristics of carbon granule type telephone transmitters.

More specifically, objects of this invention are to improve the modulation in, prevent packing of the carbon granules in, and obtain improved l non-positional performance characteristics for telephone transmitter units of the carbon granule type.

In accordance with one feature of this invention, the electrodes are provided with juxtaposed dished surfaces of such configuration that a portion of the space therebetween is restricted and the forces effective upon the carbon granules during operation of the unit are such' as to maintain the carbon in a free state. In one illustrative embodiment of this invention, the vibratile electrode has a substantially hemispherical convex surface and the other or fixed electrode has a frusto-conical concave surface coaxial with and in close proximity to the hemispherical surface.

In accordance with another feature of this invention, a portion of the granule chamber is 2 bounded by a frusto-conical wall encompassing the hemispherical surface and in juxtaposition thereto, this wall extending from the frusto-conical electrode surface and being of greater slope than this surface, thereby to produce a restriction in the chamber adjacent the hemispherical surface. As afresult, the gravitational forces effective upon the granules when the unit is held in such position that the granules would tend to fall away from the electrodes, are such as to urge the granules toward the vibratile electrode.

The invention and the above-noted yand other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which:

Fig. l is a side View in section of a transmitter uni-t illustrative of one embodiment of this invention;

Fig. 2 is a View similar to Fig. 1 of a transmitter unit illustrative of another embodiment of this invention;

Fig. 3 is a diagram showing to an enlarged scale, the configuration of the carbon granule chamber bounding elements in the unit illustrated in Fig. 1; and

Fig. 4 is a fragmentary sectional View illustrating a modication of the transmitter unit shown in Fig. 1.

Referring now to the drawing, the transmitter unit illustrated in Fig. l comprises a circular frame or foundation member IQ, for example of metal, having an internal annular fiange Il and a lat annular seating surface i2. Seated upon the surface l2 is the peripheral portion I3 of a lightweight metallic diaphragm which includes a central, shallow frusto-conical part I@ provided with stiifening corrugations or ribs I5 and includes also an annular corrugation or trough portion i6 sufciently flexible to permit bodily,

vibration of the central part M. The diaphragm, together with a moisture resistant screen or membrane Il and a multi-apertured protective cap or cover i8, is secured to the frame or foundation member l0 by an annular band I9.

Afiixed centrally to the diaphragm and vibratile therewith is a metallic electrode having a short cylindrical base portion 2% and a hernispherical portion 2l, the electrode having also a flange 22 and integral tabs 23 between which the inner edge of the diaphragm part l is clamped. Also clamped between the fiange 22 and tabs 23 are a metallic spider 2t, which serves as a lead-in conductor for the electrode, and a flexible, annular, insulating closure member 25, for

example of silk, the spider and closure member extending to the flange I and being held thereagainst by an insulating ring 26 having a frustoconical surface 29 coaxial with the vibratile electrode, and an arched surface 3U.

A back or fixed electrode 2'! is seated upon the ring 26 and is provided with a frusto-conical surface 28 coaxial with the hemispherical surface 2| and in proximity thereto. The larger end of the surface 28 is coincident with the smaller end of the surface 29 and the slope of the former surface is less than that of the latter.

The rear opening in the back electrode, through which carbon granules 3| substantially filling the chamber bounded by the two electrodes, the ring 26 and closure member 25 are introduced, is closed by a metallic cap 32 crimped over the back electrode, This electrode together with the ring 26 is locked firmly in position against the ange by a clamping band 33 which is crimped over a flange 34 on the frame and bears against an insulating ring 35 seated against the back electrode.

In order to obtain high modulation, the electrodes are placed in close proximity to one another. For example, in an illustrative construction, the minimum distance between the surfaces 2| and 28 may be substantially .039 inch. As is apparent from Fig. 3 particularly, because of the configuration and relation of the surfaces 2| and 2B, the gap between these surfaces is restricted at the region A and enlarges in both directions, i. e. toward regions B and C, from the region A. This, it has been found substantially prevents packing of the carbon granules between the electrode surfaces despite the close spacing thereof. Thus, the granules are maintained in a free state and this, together with the close spacing, assures the realization of high modulation. Also, of course, the maintenance of the good performance of the unit when, during use,

it is held in such position that the diaphragm faces upwardly and is horizontal or substantially It will be noted further that because of the configuration of the surfaces 2|, 28 and 29 and f of the fact that the surface 29 is insulating, the major portion of the current between the electrodes is directed along paths at and adjacent the region A in the gap between the electrodes. At these paths the forces, due to vibration of the diaphragm, for agitating the carbon granules are most effective, and distortion by current modulation in the transverse direction, i. e. substantially normal to the direction of diaphragm mtion, is minimized.

Distortion by such transverse modulation may be further reduced, as illustrated in Fig. 4, by heightening the frusto-conical insulating surface, thereby in effect blocking the major part of the current path normal to the axis of alignment of the two electrodes. In the construction illustrated in Fig. 4, this is effected by an insulating insert 40, having a frusto-conical surface 4|, in the back electrode, the surface 4| being coaxial with the surface 2 I.

The transmitter unit illustrated in Fig. 2 is similar to that shown in Fig. 1 and described hereinabove. However, a portion of the carbon granule chamber is bounded by a formed annular member 36, S-shaped in section and of flexible insulating material, such as silk. One end of this member is clamped between the electrode flange 22 and the diaphragm and the other end is fixed between the back electrode 2! and the annulus 3l. Because of the construction and configuration of the member 38 it will be appreciated that in use of the unit, forces tending to urge the granules into engagement with the vibratile electrode and toward the restricted space between the two electrodes are produced.

In the constructions illustrated it is to be noted that the current path between the two electrodes is of relatively small cross-section. Hence, a relatively high resistance may be obtained despite the close spacing of the electrodes.

Reference is made of the application Serial No. 783,239, filed October 3l, 1947, of Ralph R. Stevens wherein a related invention is disclosed.

Although specic embodiments of the invention have been shown and described. it will be understood that they are but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

l. A telephone transmitter comprising a xed and a vibratile electrode having juxtaposed dished surfaces one of which is convex and substantially hemispherical and the other of which is frusto-conical and has its larger end toward the hemispherical surface, means including said surfaces bounding a chamber, and comminuted resistance varying material in said chamber.

2. A telephone transmitter in accordance with claim l wherein said means comprises an insulating member having a frusto-conical surface encompassing said hemispherical surface and extending from and having its small end adjacent said rst frusto-conical surface, the slope of said second frusto-'conical surface being greater than that of said first frusto-conical surface.

3. A telephone transmitter comprising means including a pair of electrodes having juxtaposed surfaces, defining a chamber, comminuted resistance varying material in said chamber, and means for vibrating one of said electrodes, one of said surfaces being convex and domed and the other of said surfaces being frusto-conical and having its larger end nearer said one surface.

4. A telephone transmitter in accordance with claim 3 wherein said chamber defining means comprises an insulating member encompassing said domed surface and having a frusto-conical surface in juxtaposition thereto and inclined in the same direction as and of greater slope than said concave surface.

5. A telephone transmitter in accordance with claim 3 wherein said chamber defining means comprises an annular flexible insulating member, substantially S-shaped in section, encompassing said do-med surface and extending from the larger end of said concave surface.

6. A telephone transmitter comprising a diaphragm, an electrode coupled to said diaphragm and vibratile therewith, said electrode having a convex substantially hemisph'erical surface, a fixed electrode having a frusto-conical surface coaxial with said hemispherica-l surface and in juxtaposition thereto, the smaller end of said frusto-conifcal surface being away from said hemispherical surface, means including said hemispherical and frustoco=nical surfaces bounding a chamber, and -cornminuted resistance varying material in said chamber.

'7. A telephone transmitter in accordance with claim 6 wherein said chamber bounding means comprises a frusto-:coni'cal insulating wall coaxial with, encompassing and spaced from said hemispherical surface, said wall being of greater slope than said frusto-conical surface and having its smaller end coincident with the larger end of said frusto-conical surface.

8. A telephone transmitter in accordance with claim 6 wherein said chamber bounding means comp-risesy an annular flexible member of S- shaped section, coaxial with said hemispherical surface and extending between the said diaphragm and the larger end of said frusto-conical surface.

9. A telephone transmitter comprising means including a pair of electrodes and an insulating member between and spacing said electrodes, bounding a chamber, one of said electrodes having a domed portion and the other of said electrodes having a dished surface in juxtaposition to the convex face of said domed portion and having its base toward said domed portion, comminuted resistance varying material in said chamber, means for vibrating one of said e1ectrodes, and an annular insulating insert in said dishedsurface adjacent the end thereof nearest said domed portion.

10. A tele-phone transmitter comprising a first electrode having -a convex substantially hemispherical surface, a second electrode having a 85 2,225,438

frusto-conical surface coaxial with and in juxtaposition to said hemispherical surface, the

larger end of said frusto-conical surface being toward said hemispherical surface, means including said surfaces bounding a chamber, comminuted resistance varying material in said chamber, means for vibrating one of said electrodes, and an annular insulating insert in said second electrode adjacent the larger end of said frusto-conical surface, said insert having a frusto-conical surface coaxial with and opposite said hemispherical surface.

11. A telephone transmitter in accordance with claim 10 wherein the slope of said surface of said insert is greater than that of the frusto-conicai surface of said second electrode.

12. A telephone transmitter comprising a pair of electrodes having juxtaposed surfaces, means including said surfaces bounding a chamber, comminuted resistance varying material in said chamber, and means for vibrating one of said electrodes, said surfaces being dished in the same direction and of different configurations such that the spacing between said surfaces is a minimum at an intermediate region and increases in both directions from said region.

HERBERT W. BRYANT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,042,822 Bennett June 2, 1936 2,191,992 McLarn Feb. 27, 1640 Stevens Dec. 17, 19401 2,404,772 Brodie July 30, 1946 2,429,988 Bryant Nov. 4, 1947 

